1. Field of the Invention
The invention relates to pile driving, and more particularly, but not exclusively, to underwater pile driving, e.g. for stabbing piles directly into the seabed.
2. Description of the Background Art
It is known to provide a guide for aligning a pile with the surface of a substrate into which the pile is to be driven and to provide stability for a piling hammer. Particularly when piling underwater there is the problem that after the pile has been introduced into the seabed or the like, the guide must be removed to allow the pile to be driven into its final position. This guide removal is time consuming and thus expensive. Accordingly, the present applicant proposed in International patent publication WO99/11872 a pile guide which allows pile driving to continue from start to finish without any need to interrupt driving to remove the guide.
The pile driving apparatus described in WO99/11872 comprises a pile guide member which is supported on a base frame, a plan view of which is reproduced in FIG. 1. The base frame (10) has a substantially rectangular footprint (made up of a welded framework of girders and mudmats) with a centrally-placed aperture (12) through which a pile (14) is guided. The base frame 10 thus surrounds the pile (14). It will be seen however, that the base frame is formed with an aperture or slot (16) extending through the frame from its exterior to the central aperture (12) and through which a tether or rigging (18) fixed to the pile (14) can be passed.
In practice, it is important to orientate the pile so that the tether/rigging (18) will be aligned in a predetermined direction according to the intended use of the pile (14). Until now, a set pile orientation has been achieved using so-called orientation plates on the piles which engage a guide plate system in the pile guide member of the pile guide. The orientation plates are positioned on the piles in a known orientation relative to the tether/riggings couplings provided on the piles. In use, the orientation plates will engage the guide plate system as each mis-orientated pile is introduced into the pile guide member. The guide plate system forces the orientation plates to follow a helical path as the pile is further lowered through the pile guide member, causing the pile to rotate about its axis until the desired orientation relative to the base frame is achieved.
The present applicant has appreciated that more precise control of the orientation of piles being driven into a substrate (e.g. seabed) may be desirable, particularly in high swell conditions producing heave situations.
In accordance with a first aspect of the present invention, there is provided a system for controlling pile orientation comprising: a pile; and a pile guide for supporting the pile as it is driven into the substrate, comprising a base frame and a pile guide member mounted on the base frame, the pile and pile guide member having slidably interengagable profiles comprising first and second parts which are configured to axially rotate the pile to correct any mis-orientation relative to the pile guide as the parts slide past each other; characterised in that the interengaging profiles further comprise third and fourth parts which are configured to maintain a predetermined orientation of the pile relative to the pile guide once any mis-orientation has been corrected by interengagement of the first and second parts.
The third and fourth parts prevent the orientation of the pile from changing after the first and second parts have cleared each other as the pile is driven into the substrate. The third and fourth parts may be configured to engage each other before the first and second parts slide past and disengage each other. In this way, there is no risk that the predetermined orientation of the pile will not be maintained when the first and second parts disengage. This may be particularly important in heave situations which may produce periodic upward movements in the pile relative to the pile guide. In the conventional arrangement, once the first and second parts have slid past one another, any new mis-orientation in the pile may cause the first and second parts to jam against each other during heave-induced, relative upward movement.
The interengagable profiles (e.g. second and fourth parts) on the pile guide may be contiguous or may be spaced apart. The interengagable profiles (e.g. first and third parts) on the pile are spaced apart along the length of the pile.
The third and fourth parts may comprise a plate-like member and a channel in which the plate-like member is a sliding fit. The plate-like member may be mounted on the pile, and the channel may be provided on an inner periphery of the pile guide member.
The channel may have an upper flared opening for first receiving the plate-like member as the pile is lowered through the pile guide. The channel may also have a lower flared opening for re-engaging the plate-like member if the pile rises up through the pile guide (e.g. during heave situation).
The channel may be formed between a pair of spacer plates, the spacer plates being configured to centre the pile in the pile guide member.
The first and second parts may comprise an orientation plate and a guide plate system defining a helical pathway for the orientation plate. The orientation plate may be mounted on the pile, and the guide plate system may be provided on an inner periphery of the pile guide member. The guide plate system may define a pair of helical pathways of opposite senses of rotation, which define a tapering channel therebetween for correcting any mis-orientation in the pile. The tapering channel may have a flared portion at its lower end for re-capturing the orientation plate should the pile move upwards relative to the pile guide after the first and second parts have slid past each other.
In another aspect of the present invention, there is provided a pile for driving into a substrate, the pile comprising: an elongate body with a leading end and a trailing end; a coupling for receiving a tether, the coupling being located towards the trailing end; a first member projecting radially outwardly from the body, the first member being located towards the leading end; and a second member projecting radially outwardly from the body, the second member being axially spaced towards the trailing end from the first member.
The coupling may be angularly offset (e.g. 90°) relative to at least one member. The first and second members may be angularly aligned. The first member and/or the second member may be plate-like with the plane of the or each member parallel to the longitudinal axis of the body.